I have a '97 Expedition with just over 50k - same problem for years, but it finally got to the point where I could not take the noise. I just bought a needle grease attachment to put on my hand pump grease gun - it's like a hypodermic meant for injecting grease into 'sealed' ball joints and other steering components by piercing the rubber boot (those without a standard grease fitting). I used the better part of a tube of grease and injected it into the ball joints and any other sealed joints until it was just coming out around the joint - took it for a spin to move the grease around and it completely eliminated the noise. I just wish I had done it years ago. I was quite surprised at how much grease they took - I wonder how much Ford puts in the sealed units? I never did understand why the auto industry got rid of grease fittings on factory components, but you can usually get them on the replacement parts. The better to sell you new ball joints, perhaps ! ? !